Technical Field
The present invention relates to a charged particle beam system and more particularly to a charged particle beam system suitable to a cancer treatment using an ion beam such as a proton, a helium ion, or a carbon ion.
Background Art
A charged particle beam irradiation system for irradiating an ion beam such as a proton, helium, or carbon to a tumor volume of a patient to treat a cancer includes an ion source, an accelerator, a beam transport system, and a rotating gantry and the rotating gantry includes an irradiation nozzle for irradiating the ion beam to the patient.
The ion beam generated by the ion source is accelerated up to desired energy using the accelerator such as a synchrotron or a cyclotron and then is extracted from the accelerator to the beam transport system. The extracted ion beam is transported to the irradiation nozzle installed in the rotating gantry by the beam transport system. The rotating gantry is rotated, so that the irradiation nozzle is rotated around a rotation axis of the rotating gantry and is aligned with the irradiation direction of the ion beam with respect to the tumor volume of the patient on a treatment couch. Therefore, the tumor volume (the target volume) is irradiated with the ion beam transported to the irradiation nozzle in the irradiation direction set by the rotating gantry in accordance with a depth of the tumor volume, which is an irradiation target of the ion beam, from a body surface and with a shape of the tumor volume.
An ion beam irradiation method using the irradiation nozzle can be broadly divided into a scatterer method and a scanning method. In the scatterer method, the ion beam is enlarged in a lateral direction of the tumor volume, which is an irradiation target, by a scatterer, and also enlarged in a depth direction of the tumor volume by using an SOBP (spread out of Bragg peak) filter. The tumor volume is irradiated with the enlarged ion beam. In the scanning method, in accordance with the shape of the target volume, the ion beam is moved in the lateral direction of the tumor volume by using a scanning magnet and in the depth direction of it by changing the energy of the ion beam is changed by the accelerator and the whole tumor volume is irradiated with the ion beam (refer to Japanese Patent Laid-Open No. 10(1998)-118204 and Japanese Patent Laid-open No. 2004-358237).
When a human body is irradiated with the ion beam, the dose distribution as shown in FIG. 3 of Japanese Patent Laid-Open No. 10(1998)-118204 is shown in the depth direction of the human body, and the dose is maximized at the Bragg peak. Furthermore, the dose distribution reduces rapidly at a depth exceeding the Bragg peak. The cancer treatment using the ion beam uses the property that the dose is maximized at a depth exceeding the Bragg peak and the dose reduces rapidly at a depth exceeding the Bragg peak.
Japanese Patent Laid-open No. 2010-32451 describes that in one charged particle beam irradiation system, ion beams different in kind, that is, a proton ion beam (a proton beam) and a carbon ion beam (a carbon beam) are switched and the tumor volume of the patient is irradiated with the proton ion beam or the carbon ion beam. Japanese patent No. 4632278 describes that in one charged particle beam irradiation system, ion beams different in kind, that is, any of a helium ion beam, a carbon ion beam, and an oxygen ion beam is injected into the synchrotron which is an accelerator, and the injected ion beam is accelerated by the synchrotron, and then the tumor volume of the patient is irradiated with any of these accelerated beams.
H. Eickhoff et al., GSI Darmstadt, “TESTS OF A LIGHT-ION GANTRY SCECTION AS AN EXAMPLE OF PREPARATIONS FOR THE THERAPY FACILITY IN HEIDELBERG”, Proc. of EPAC 2002, Paris France describes similarly to Japanese Patent Laid-open No. 2010-32451 and Japanese patent No. 4632278 that in one charged particle beam irradiation system, a plurality of kinds of ion beams are switched and an irradiation target is irradiated with the switched ion beam.